1. Field of the Invention
This invention relates generally to semiconductor fabrication, and, more particularly, to modifying process selectivities based on process state information.
2. Description of the Related Art
Chemical and/or mechanical techniques may be used to remove material from wafers during semiconductor processing. For example, etching techniques may be used to remove selected portions of one or more layers deposited above a substrate to form structures, such as gates, vias, trenches, and the like. For another example, chemical mechanical polishing techniques may be used to polish and/or planarize a surface of a layer deposited above the substrate. The rate at which the chemical and/or mechanical techniques remove material typically depends on parameters associated with the removal technique. For example, etching rates may depend on parameters such as the concentration and/or composition of the etchant, the ambient temperature and/or pressure, and the like. For another example, chemical mechanical polishing rates may depend on the concentration and/or pH of the slurry compound, a spin rate of a platen, and the like.
Material removal rates also depend upon the chemical composition of the material being removed. For example, an etching technique may remove silicon dioxide at a first rate and the same etching technique may remove silicon nitride at a second rate that is about 10 times slower than the first rate. The relative rate at which a given technique removes different materials is commonly referred to as the “selectivity” of the technique. For example, the selectivity of the etching technique described above to silicon dioxide and silicon nitride is about 10:1. Selecting an appropriate selectivity may substantially improve processing of a semiconductor wafer. For example, when a silicon dioxide layer is being etched, overetching of a silicon nitride layer that is formed beneath the silicon dioxide layer may be reduced by using an etchant that has a relatively large silicon-dioxide-to-silicon-nitride selectivity.
The selectivity of a material removal technique, such as etching or chemical mechanical polishing, is usually determined based on wafer state measurements. For example, a silicon dioxide layer may be deposited above a wafer and polished using a chemical mechanical polishing technique. Before and after thicknesses of the silicon dioxide layer may be determined using metrology and used to determine the silicon dioxide removal rate for the chemical mechanical polishing technique. A silicon nitride layer may be deposited above another wafer and polished using the same chemical mechanical polishing technique. Before and after thicknesses of the silicon nitride layer can be used to determine the silicon nitride removal rate for the chemical mechanical polishing technique. The silicon dioxide and silicon nitride removal rates may then be combined to determine the selectivity of the chemical mechanical polishing technique.
Conventional techniques for determining selectivities using wafer state measurements are time-consuming and reduce the throughput of the semiconductor fabrication facility. One method for improving the efficiency of conventional selectivity determination techniques uses process state sensors to identify process endpoints where selectivities are more likely to change. For example, optical emission spectroscopy may be used to detect an endpoint of an etching or chemical mechanical polishing process. Once the endpoint has been reached, the selectivity may be determined using the conventional multi-wafer process described above. However, these selectivity determination techniques may still reduce the throughput of the semiconductor fabrication facility.
The present invention is directed to addressing the effects of one or more of the problems set forth above.